1. Technical Field
The present invention generally relates to an optical instrument and more particularly, to an optical unit provided with a driving transmission shaft which may be disengaged from a corresponding driving transmission shaft of a mating instrument, in association with the detachment of the mating instrument from the optical unit for example, as in an automatic focusing system camera which is so arranged that a driving force for focusing control can be transmitted from a camera main body to an interchangeable or exchangeable lens (referred to as an exchangeable lens hereinafter).
2. Prior Arts
An automatic focusing camera is known, which is arranged to transmit a focusing control driving force produced from the interior of a camera main body to a focusing system provided in an exchangeable lens barrel with a lens system driving shaft arranged to be projected from or retreated into a mounting surface of the camera main body, and a driven shaft of the exchangeable lens barrel. In such automatic focusing camera, it is required, for the detachment of the exchangeable lens barrel, that the driving shaft also be released from the driven shaft when a position restricting member adapted to be projected from or retreated into the mounting surface of the camera main body is released from a position restricting recess in the exchangeable lens barrel by operating a lock releasing member.
However, in the known cameras of the above described type, since a sufficient consideration has not been given to the relation between the retreating movement of the position restricting member into the camera main body and the retreating movement of the driving shaft it is possible that the following problems could arise during detachment of the exchangeable lens barrel.
(a) For example, where the optical system driving shaft still projects slightly from the mounting surface of the camera main body when the position restricting member has been retreated to a position sufficient for the detachment, if the exchangeable lens barrel is unduly rotated or revolved when detached, not only the mounting surface of the lens barrel is damaged, but it may be impossible to detach the lens barrel, with the driving shaft remaining engaged with an end of the driven shaft for the exchangeable lens barrel in these instances where the drive shaft projects outwardly to a large degree. (b) In this situation, the rotational force for the detachment is applied to the end of the driving shaft and a clutch portion at the forward end of the driven shaft so as to cause possible damage at such portions, thus resulting in an inconvenience in the engagement of the clutch thereafter.
(c) Also, where the amount or length of retreatment of the driving shaft from the mounting surface of the camera main body is smaller than the amount or length of retreatment of the position restricting member, the following problems occur. When the rotating operation is effected for detachment with both the position restricting member and the driving shaft retreated from the mounting surface, if the operation by the lock releasing member is removed in the course of rotation, the optical system driving shaft is released from the retreatment so as to contact the mounting surface of the exchangeable lens barrel under high pressure. Therefore, if the rotation for the detachment is further continued, the mounting surface of the exchangeable lens barrel is undesirably damaged by the end of the driving shaft.
The optical system driving shaft in the camera main body is arranged to be advanced or retreated as described above, but similarly take place when the lock releasing member and the position restricting member are provided in the exchangeable lens barrel, with the driven shaft being adapted to be advanced or retreated with respect to the camera main body.
In FIGS. 5 through 10 of U.S. Pat. No. 449,807, commonly owned herewith there is provided a mount positioning recess 64, and a driven shaft 60 is associated with the optical systems 52 and 53 in the mounting portion of an interchangeable lens 2. The forward end portion of the driven shaft 60 projects from the bottom face of the recess 64 to an extent that it does not extend outwardly from the mounting surface. Meanwhile, at the mounting portion of the photographic camera main body 1, the mount positioning member 9 is supported so as to be movable between the projecting position where it projects from the mounting surface and is fitted into the recess 64 and the retreating position where it is retreated into the mounting surface, and is urged towards the projecting position by a spring 15. On the other hand, the driving shaft 13 is disposed within the positioning member 9, and is arranged to be normally movable together with the member 9 as one unit between the engaging position where it is engaged with the driven shaft 60 and the disengaging position where it is spaced from the driven shaft 60. In the camera described above, since the flange 33 of the shaft 13 contacts the stepped portion 38, there is no possibility that the forward end of the shaft 13 projects beyond the forward end of the member 9. Accordingly, when the end of the member 9 is retreated from the mounting surface, the end of the shaft 13 has been retreated from the mounting surface without fail.
However, in this known photographic camera, it is necessary that the member 9 project to an extent greater than the length of projection required for the engagement at the shafts 13 and 60. Therefore, the amount of operation of the mount release button 7 as a manual member necessary for causing the member 9 to be retreated from the mounting surface, is undesirably increased. Meanwhile, at the lens barrel side, a deeper recess must be formed compared to a depth necessary for the positioning.